Abstract
Switching dynamics of perpendicular magnetic tunnel junction (MTJ) driven by spin–orbit torque (SOT) are investigated by the Landau–Lifshitz–Gilbert (LLG)-based physical model considering the temperature dependence. The field-assisted switching method is proposed to develop the reliable sub-ns writing of SOT-magnetoresistive random-access memory (SOT-MRAM) by removing the plateau time. The conventional method of SOT-MTJ requires the large write current, leading to the area increase of access transistors and the penalty of memory density. The write current and the switching time of SOT-MTJ can be efficiently reduced at the same time by our field-assisted method using the enhanced magnetic field. The magnetic field can be provided by the Co magnetic hard mask above the MTJ. Considering an SOT-MRAM array, the surrounded Co metals have the insignificant influence of stray magnetic field on an MTJ at the center. With the write time of 0.2 ns, the 60% reduction of write current is achieved by our field-assisted method compared to the conventional method. The required write current for the SOT switching decreases with the increasing temperature due to the lowering of thermal stability factor. The write Shmoo plots are further analyzed to calculate the write current margin at the various working temperature. The write time of 0.2 ns exhibits the narrow margin of write current ( $2.6~\mu \text{A}$ ) in the temperature range from 25 °C to 85 °C, while the write time of 0.8 ns has the wide write margin of $102~\mu \text{A}$ . The switching behavior and the write margin are also sensitive to the magnetic field.
Highlights
M AGNETORESISTIVE random-access memory (MRAM) is a promising candidate among emerging memories for the microcontroller unit [1], automotive applications [2], and cache replacement [3] due to its fast switching, high endurance, and low energy consumption
In the write_1 operation (P to AP switching), with ISOT of 600 μA and the write time of 1 ns [see Fig. 2(c)], the magnetization can be driven to the −y-axis by the spin Hall effect (SHE) torque [see Figs. 2(a) and 3(a) and (b)]
Note that the magnetization of the free layer is parallel or antiparallel to the magnetization of the pinned layer in spin–transfer torque (STT)-magnetic tunnel junction (MTJ), and this leads to the minimum initial spin torque and the large incubation delay
Summary
M AGNETORESISTIVE random-access memory (MRAM) is a promising candidate among emerging memories for the microcontroller unit [1], automotive applications [2], and cache replacement [3] due to its fast switching, high endurance, and low energy consumption. The field-assisted method of SOT switching is proposed to remove the plateau time and decrease the write current. The x-direction magnetic field (Hx ) [see Fig. 1(b)] is required to break the symmetry of SOT-driven perpendicular MTJ [23].
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